The present invention relates to the field of “medical devices” as may be defined, for example, by the Jun. 14, 1993 directive 93/42/CE of the European Communities. The present invention may also relate to the “active implantable medical devices” field as defined, for example, by the Jun. 20, 1990 directive 90/385/CEE of the European Communities.
Such devices may include implantable medical devices that continuously monitor a patient's cardiac rhythm and deliver electrical pulses to the heart for cardiac stimulation, resynchronization, cardioversion, and/or defibrillation in case of a rhythm disorder detected by the device. Such devices also include neurological devices, cochlear implants, etc., as well as devices for pH measurement or devices for intracorporeal impedance measurement (such as the measure of the transpulmonary impedance or of the intracardiac impedance). The invention particularly relates to autonomous implanted capsules and are free from any physical connection to a main implanted device (for example, the can of a stimulation pulse generator).
Recent advances in microfabrication and biotechnology have allowed the development of a wide variety of such miniaturized implantable devices, providing physicians with less invasive implantation procedures, providing more comfort for patients, providing increased performance, and providing access to new types of diagnostics and treatments.
The invention also relates to autonomous capsules implanted without any physical connection to a main device (e.g., a stimulation pulse generator). These autonomous capsules may be called “leadless capsules” to distinguish them from the electrodes or sensors placed at the distal end of a lead.
Implants without lead or leadless capsules are for example described in U.S. 2007/0088397 A1 and WO 2007/047681 A2 (Nanostim, Inc.) or in the U.S. 2006/0136004 A1 (EBR Systems, Inc.).
The leadless capsules can be e.g. epicardial capsules fixed to the outer wall of the heart, or endocardial capsules, fixed to the inner wall of a ventricular or atrial cavity through a projecting anchoring screw axially extending the capsule body and for penetrating into the cardiac tissue by screwing at the implant site. The invention is more specifically dedicated to endocardial capsules.
A leadless capsule includes sensing/pacing circuits to collect myocardium depolarization potentials and/or to apply stimulation pulses to the site where the capsule is implanted. The latter includes then an appropriate electrode which can be formed by an active portion of the anchoring screw. It can also, alternatively or in addition, incorporate, one or more sensors to locally measure the value of a parameter such as the level of oxygen in the blood, the heart intracardiac pressure, the acceleration of the heart wall, the acceleration of the patient as an indicator of activity, etc.
The leadless capsules also incorporate transmitter/receiver wireless communication means to remotely exchange data.
Whatever the implemented technique, the signal processing within the capsule and its remote transmission requires significant energy compared to energy resources that can store the capsule. However, due to its autonomous nature, the capsule can only use its own resources such as an energy harvesting circuit associated with a small integrated buffer battery.
Energy harvesting systems for leadless capsules have been proposed. However, such systems rarely provide enough power to supply a regular capsule. Moreover, keeping a capsule with an energy harvester small is a challenge.
Following the examples of U.S. Pat. Nos. 6,984,902 and 7,843,090, the majority of energy harvesting systems today are based on an inertial device, that is to say, using the acceleration of the environment to act on a mass, known as “seismic mass”, whose relative movement with respect to a piezoelectric electromagnetic or electrostatic transducer, generates an electrical magnitude.
The U.S. Pat. Nos. 7,729,768, 3,456,134 and U.S. 2010/0217364 proposes a configuration in which an inertial harvester in which an oscillating seismic mass and associated energy harvesting methods are disposed in a chamber, within a housing of a leadless capsule. This mass can be driven in at least one degree of freedom by the overall movement of the capsule, which allows harvesting methods to convert movement of the seismic mass relative to the housing into electrical energy. The amount of converted energy is proportional to the mass and thus the volume of the seismic mass, and is directly related to the amplitude of the vibration acceleration to which the mass is subjected. The capsule is in direct contact with the heart tissue via a rigid base.
The U.S. 2007/0293904 A1 discloses a further energy harvesting device, wherein the variations of blood pressure deform a bellows-shaped housing anchored to the cardiac wall, with resonance of an oscillating mass controlling a piezoelectric or electromagnetic generator.
An object of the invention is to provide a leadless capsule that would simultaneously harvest energy from seismic mass movements of the walls of organs and from the forces (e.g., turbulences) of fluid flows (e.g., blood flow) while retaining a small size.
Some embodiments achieve this object with an autonomous intracorporeal medical capsule including a housing defining a chamber in which an oscillating seismic mass and harvesting methods to convert a relative movement of the seismic mass relative to the housing into electrical energy. The capsule further includes methods for anchoring the housing to a wall of an organ of a patient. The capsule further may include an elastically deformable base connected to the housing at a first end and carrying the anchoring at a second end.
From a dynamic point of view, the seismic mass of the capsule according to the invention is subject to the forces provided by movements of the organ wall that are transmitted by the base. According to the invention, the seismic mass is further subject to fluid forces on the capsule, due to the fact that the elasticity of the base allows the housing to move relative to the wall. In the prior art, this fluid component is not present because the base is rigid and is intended to severely restrict the movement of the housing.
It is therefore possible to harvest both the mechanical energy of the movements of the walls of organs and that provided by the fluid flow, without the need to increase the weight or volume of the seismic mass.
Another advantage of the invention relates to the anchoring of the capsule. In the prior art, the capsule is rigidly attached to the wall, resulting in the forces and turbulence of blood flow exerted on the capsule being mechanically transmitted to the anchoring point in the cardiac wall. These forces end to weaken the system, with the risk of tearing the capsule. With the invention, this risk is reduced by the elasticity of the base, which is advantageously able to absorb applied fluid forces without transmitting them to the tissue anchor.
As discussed in more detail below, the inertial system formed by the capsule according to the invention can be modeled by two coupled oscillators, one formed by the seismic mass oscillating in the housing, and the other by the housing itself oscillating relative to the organ wall at the end of the elastically deformable base.
The spectrum of the relative displacement of the seismic mass has a wider frequency band resulting in a more effective energy harvesting. According to some embodiments of the invention, the mass and the coefficients of restoring forces of the seismic mass and of the housing are selected such that the displacement of the seismic mass relative to the capsule housing has a first maximum between 0.5 and 10 Hz and a second maximum between 12 and 40 Hz. This advantageous arrangement has the effect of aligning the frequency of the maxima of the spectrum of the relative displacement of the seismic mass with typical frequency intervals of blood flow pulses (0.5 to 10 Hz) and of motion of the heart walls (15 to 40 Hz).
In a particular exemplary embodiment, the first maximum is 1.2 Hz and the second maximum is located at 18 Hz.
According to a first embodiment, the seismic mass and the base are configured so that the oscillating movement of the seismic mass and the deformation movement of the base are made in longitudinal main directions, oriented perpendicularly to the wall of the organ of the patient. According to a second embodiment, the seismic mass and the base are configured so that the oscillating movement of the seismic mass and the deformation movement of the base are made in transverse main directions, oriented parallel to the wall of the organ of the patient.
One or both oscillating elements may be or include a spring such as a spiral spring, a helical spring, or an elastic girder.
The capsule according to the invention may include provisions for reversible attachment of the housing on the base. In such embodiments, it may be advantageously easy to replace the capsule without removing the anchor from the cardiac tissue.
An autonomous intracorporeal capsule is shown and described. A housing defines a chamber in which an oscillating seismic mass and an energy harvesting device are arranged. The energy harvesting device converts relative movement of the seismic mass to energy. The capsule also includes an anchoring device for coupling the housing to the wall of an organ of a patient. The capsule further includes an elastically deformable base connected to the housing at a first end and carrying the anchoring at a second end.
One embodiment relates to an intracorporeal medical capsule. The capsule includes a housing defining a chamber. The chamber houses an oscillating seismic mass and an energy harvester that converts movement of the seismic mass relative to the energy harvester into electrical energy. The capsule further includes an anchor for anchoring the housing to a wall of an organ of a patient. The capsule also includes an elastically deformable base between the housing at a first end and the anchor at a second end. The masses (m1, m2) and the elastic coefficients (k1, k2) of the seismic mass and of the housing may be such that the spectrum of the relative movement (U) of the seismic mass relative to the housing has a first maximum between 0.5 and 10 Hz and a second maximum between 15 and 40 Hz. The first maximum may be 1.2 Hz. The second maximum may be 18 Hz. The coefficients (k1, k2) of the restoring forces of the oscillating seismic mass and of the housing may have a ratio equal to 1. The seismic mass and the base may be located so that the oscillating movement of the seismic mass and the deformation movement of the base are coaxial and are perpendicular to the wall of the patient's organ. The seismic mass and the base may be located so that the oscillating movement of the seismic mass and the deformation movement of the base may be transverse main directions oriented parallel to the wall of the patient's organ. The elastically deformable element provides for oscillation of the seismic mass. The elastically deformable element may be or include at least one of: a cantilever beam, an engraved spring, and a spiral spring. The elastically deformable base may be or include at least one of: a coil spring and a cantilever beam. The capsule further includes methods for reversible attachment of the housing on the base.
Another embodiment relates to an intracorporeal medical capsule. The capsule includes an elastically deformable base having an anchor at one end and coupled to a capsule body at the opposite end. The capsule further includes an energy harvesting element elastically coupled to a seismic mass within the capsule body. The elastically deformable base increases energy harvested at the energy harvesting element due to elastic movement of the capsule body in the presence of blood flow around the capsule body.
Another embodiment relates to a method for harvesting energy in an intracorporeal medical capsule for a heart. The method includes anchoring an elastically deformable base to a wall of tissue within the heart. The method further includes receiving mechanical energy via movement of the wall, a seismic mass elastically coupled inside the capsule to an energy harvesting element. The method further includes receiving mechanical energy via movement of blood in the heart using the elastically deformable base. The method also includes utilizing, by the energy harvesting element, the mechanical energy received via the movement of the wall and the mechanical energy received via the movement of blood in the heart.